1. Field of the Invention
Rising atmospheric temperature, i.e. global warming has come to pose a serious social issue in recent years. The carbon dioxide emanating from factories and other industrial facilities is believed to be one of the main causes for this phenomenon. Solving this problem of the g1obal warming will require a technique for recovering and fixing the carbon dioxide which has already been released into the air and a technique for separating and recovering high-concentration, high-temperature carbon dioxide from waste gas sources before it is released into the atmosphere. An organic separation medium is unsuitable for the separation and recovery of hot carbon dioxide because of its unreliable thermal resistance. As a result, ceramics, which are well known for thermal stability, are promising candidates for separation media. This invention aims to provide a method for the separation of nitrogen and carbon dioxide by means of sepiolite, a clayish mineral. It is believed to be capable of contributing immensely to the preservation of the environment on a global scale.
2. Description of the Prior Art
As a means to separate and recover hot carbon dioxide from waste gases such as from factories and plants by the use of a ceramic separation medium, the present inventors previously developed a method which uses sepiolite in its unmodified form or sepiolite which has undergone an ion-exchange treatment with zinc and filed a patent application covering this invention (U.S. application Ser. No. 08/339238). This method resides in separating nitrogen and carbon dioxide by utilizing the fact that these two gases exhibit different adsorption properties to sepiolite. When sepiolite is heated to an elevated temperature exceeding 200.degree. C., it undergoes a phenomenon called folding which causes part of the minute channel-like holes in the sepiolite to collapse. As a result, the area of contact of the sepiolite with gaseous components decreases and the capacity thereof as a separation medium declines proportionately. Practically, therefore, it is desired to develop an improved method for separating hot carbon dioxide and nitrogen under an elevated temperature. This invention provides an improvement which enables sepiolite to maintain its ability as a separation medium (by precluding the minute channel-like holes thereof from collapsing) even at elevated temperatures.